Printing systems utilizing lasers to reproduce information are well known in the art. These printing systems typically use one or more Raster Output Scanners (ROS) to expose the charged portions of a photosensitive medium, such as a photoreceptor, to record an electrostatic latent image. The photosensitive medium is exposed to a toner, which is attracted to the electrostatic latent image. The toner may then be transferred to the print medium, such as sheet of paper, to reproduce the image.
Typically, an ROS will build the electrostatic latent image onto the photosensitive medium using a series of scan lines. Printing systems may also use multiple ROS units to form the image on the photosensitive medium. For example, color printing systems may use a plurality of ROS units, where each ROS forms a scan line for a separate color. Thus, it is important that the ROS units operate precisely and accurately. For example, registration of each scan line of ROS units in a color printing system can be required to be within a 0.1 mm circle or within a tolerance of .+−.0.05 mm.
Ideally, a ROS should be capable of exposing a line of evenly spaced, identical pixels on the photosensitive medium. In order to form these pixels, a ROS focuses its light beam into a spot along a scan line on the photosensitive medium. The speed at which a ROS scans along a scan line is known as the spot velocity.
However, the inherent geometry of the optical system used in a ROS makes obtaining evenly spaced, identical pixels problematic. Common manufacturing variances and errors may also cause inaccuracies by an ROS. These shortcomings in a typical ROS result in errors known as “scan non-linearity.” Scan non-linearity refers to the deviations in uniform pixel placement by a ROS along a scan line.
Scan non-linearity results in a poorer image quality. For example, scan non-linearity can cause mis-registration between colors in a multiple ROS laser printer. Therefore, many known systems include scan non-linearity correction mechanisms.
Unfortunately, such correction mechanisms can be difficult to implement. For example, the non-linearity signature varies from ROS to ROS. Thus, each ROS must be separately measured and adjusted by a technician to correct its scan non-linearity. This calibration process can also be tedious and time consuming. In addition, over the lifetime of operation, the scan non-linearity of a ROS may vary or change. This may render the implemented correction obsolete or ineffective.
Accordingly, it would be desirable to provide methods and systems that are capable of efficiently correcting scan non-linearity in a ROS. In addition, it would be desirable to provide an efficient process for calibrating a ROS to correct or minimize its scan non-linearity.